When calculating the moment around D, I think it should be (R x Fac SinO) in other word ( radius vector X force AC X sinO) the angle theta is the one between the radius vector and the force. In this case I would say:Md=(-26*300)+(6*ac3/sqr10)
I am surprised that it is not in the playlist, also. These were created so long ago (last time I taught Statics), that I do not recall how many of the inclass examples were also posted. Entirely likely that it simply was not done. Or, it sits somewhere else and just wasn't added to the playlist.
